1. Field of the Invention
This invention relates to vehicular semi-automatic mechanical transmission systems and, in particular, to semi-automatic mechanical transmission systems of the type providing partially automatic implementation of manually or automatically selected changes or shifting of mechanical transmission gear ratios.
More particularly, the present invention relates to a control system which enhances recovery from missed shifts in a semi-automatic shift implementation requiring the vehicle operator or system controller to create synchronous or substantially synchronous conditions for engagement of the transmission nonsynchronized jaw clutches.
2. Description of the Prior Art
Fully automatic transmission systems, both for heavy-duty vehicles such as heavy-duty trucks, and for automobiles, that sense throttle openings or positions, vehicle speeds, engine speeds, and the like, and automatically shift the vehicle transmission in accordance therewith, are well known in the prior art. Such fully automatic change gear transmission systems include automated transmissions wherein pressurized fluid is utilized to frictionally engage one or more members to other members or to a ground to achieve a selected gear ratio as well as automated mechanical transmission utilizing electronic and/or pneumatic logic and actuators to engage and disengage mechanical (i.e. positive) clutches to achieve a desired gear ratio. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 3,961,546; 4,081,065 and 4,361,060, the disclosures of which are hereby incorporated by reference.
Such fully automatic change gear transmissions can be unacceptably expensive, particularly for the largest heavy-duty vehicles which are not typically sold in high volumes. Additionally, those automatic change gear transmissions utilizing pressurized fluid and/or torque converters tend to be relatively inefficient in terms of power dissipated between the input and output shafts thereof.
Semi-automatic transmission systems utilizing electronic control units which sense throttle position, engine, input shaft, output shaft and/or vehicle speed, and utilize automatically controlled fuel throttle devices, gear shifting devices and/or master clutch operating devices to substantially fully automatically implement operator manually selected transmission ratio changes are known in the prior art. Examples of such semi-automatic transmission systems may be seen by reference to U.S. Pat. Nos. 4,425,620; 4,631,679 and 4,648,290, the disclosures of which are incorporated herein by reference.
While such semi-automatic mechanical transmission systems are very well received as they are somewhat less expensive than fully automatic transmission systems, allow manual clutch control for low speed operation and/or do not require automatic selection of the operating gear ratio, they may be too expensive for certain applications as a relatively large number of sensors and automatically controllable actuators, such as a master clutch and/or a fuel throttle device actuator, are required to be provided, installed and maintained.
Semi-automatic shift implementation systems/methods for mechanical transmission systems for use in vehicles having a manually only controlled engine throttle means, and a manually only controlled master clutch, have been proposed. Such systems may be seen by reference to U.S. Pat. Nos. 5,053,959; 5,053,961; and 5,053,962, the disclosures of which are incorporated herein by reference.
These systems may include a control/display panel or console for operator selection of upshifts, downshifts or shifts into neutral, an electronic control unit (ECU) for receiving input signals indicative of transmission input and output shaft speeds and of manually selected shifts and for processing same in accordance with predetermined logic rules to issue command output signals and a transmission actuator for shifting the transmission in accordance with the command output signals. The control/display device will allow the operator to select/preselect a shift into a higher ratio, a lower ratio or into neutral and will display the selected but not yet implemented shift as well as the current status of the transmission.
A concern with such automated and semi-automated systems, especially semi-automatic mechanical transmission system requiring an operator to manually bring the transmission within an acceptable range of synchronous conditions before the control allows or commands engagement of a target gear ratio, is that the ranges are set at relatively small bands, to increase shift quality, which may result in the operator missing the band and becoming stuck in neutral, which is usually very understandable.
According to the control of U.S. Pat. No. 5,063,511, the disclosure of which is incorporated herein by reference, if the selected shift is not implemented within a given period of time, the control logic will assume that the operator has missed the shift and will increase the bands or ranges to allow for a harsher shift which enhances the probability that the operator's efforts will result in implementation of the selected shift.
While the missed shift recovery system/method of above-mentioned U.S. Pat. No. 5,063,551 does considerably enhance the probability of recovering from a missed shift from neutral into a desirable target ratio, a shift into the selected desirable target ratio may remain unaccomplished.